“Love is not love which alters when it alteration finds,” wrote William Shakespeare in his 116th Sonnet. “O no! it is an ever-fixed mark that looks on tempests and is never shaken.”

Nothing could be further from the truth, says the new science of romantic love.

Love is, first and foremost, an emotion—but one that is, more than most emotions, rooted in our bodies. I’m not just referring to lust, though that can lead to romantic love. As love grows and deepens, it lights up some parts of our nervous systems and dims others. The importance of feel-good hormones like oxytocin and dopamine may decline over the course of a relationship—but a love that reaches maturity will bind the lovers on a neurological level.

Far from an “an ever-fixed mark,” love is a process subject to biological forces beyond our conscious control. Drawing from new research by Cal psychologist Dacher Keltner, along with Barbara Fredrickson, John Gottman, Helen Fisher, Kayt Sukel (author of Dirty Minds), and many neuroscientists, here is a list of the places where love abides in our bodies — and the role each one plays in sustaining love over time. Just in time for Valentine’s Day!

When sexual pursuit begins, the brain releases a class of hormone called androgens, including testosterone — which, yes, also happens in women when they see something they want. In fact, as Helen Fisher points out, women produce more new testosterone than men when they compete for a prize. And in the bodies of both men and women, sex raises testosterone counts. So with the right person, the more sex you have, the more sex you want—and the more willing you are to chase after it. Learn more about the effects of testosterone.

Can’t get enough: Orgasms

Orgasm consumes as many as 30 parts of the brain, including those involved in touch, fantasy, memory, and reward. As you can see in this image of an orgasm Kayt Sukel experienced in a brain scanner, the climax burns through the brain like wildfire, setting alight the prefrontal cortex and anterior cingulate cortex (while smothering other parts, like the left orbitofrontal cortex, which is involved in decision making).

Orgasm releases serotonin and opioids whose chemicals we also find in heroin—thus it is no surprise that sex with the right person can become addictive. Get some sex tips for men.

Judgement fails: The amygdala

There’s an old region near the brainstem called the amygdala. That’s the threat-detector—it starts firing when you see danger, risk, and uncertainty. When you’re in the intense throes of romantic love, the amygdala sleeps, as do parts of the frontal lobe, which involves judgment. The upshot is that the brain in love is prone to bad decisions—it has trouble detecting threats (like jealous spouses) and connecting actions with long-term consequences (like the effects of unprotected sex). Learn more about the amygdala.

Trust and devotion grow: Oxytocin

As the brain moves from lust to love, the ventral pallidum activates. Our blood is flooded with the neurotransmitter oxytocin, which has been shown to increase generosity and empathy. Women already have a lot of oxytocin, but studies show that men get a big surge in it after a long, passionate kiss; it’s one of the biological forces that moves them away from pure lust toward care, trust, and devotion. This is also true of rodents—if you give a promiscuous vole a little dose of oxytocin, it becomes monogamous. Learn more about oxytocin.

As positive psychologist Barbara Fredrickson has described, heart rhythms, facial expressions, and hand gestures begin to synchronize in long-term lovers—a process largely regulated by the vagus nerve, which winds from the brain to the heart. This neurological alignment enables us to detect trouble or pain in our beloved when no else can.

And as lovers tune in to each other, they become more willing and able to make sacrifices for the relationship. Research finds that if sacrifice comes out of a desire to alleviate suffering in our spouses, we get many mental and physical health benefits.

Touch is “our primary language of compassion,” says Dacher Keltner, “and a primary means for spreading compassion.” Touching in couples increases happiness and lowers stress levels, but there are some gender differences in how touch is perceived: Dacher’s research shows that women aren’t always able to feel the compassion in a man’s touch, and men are often slow to pick up on anger in a woman’s touch.

“When Men Are Involved in the Care of Their Infants, the Cultures Do Not Make War” by John Gottman is one of the best recommendations for perpetuating quality of life there is. It is a cultural value we can all practice as couples, we do not have to depend on other people to implement.

Others cultural values that we must practice daily to produce and perpetuate quality of life:

… Men must Listen to our Wives very carefully, wives have more empathy, common sense and intuition than men

… Share with the Poor

… Promote “Peace On Earth” and Live by the “Golden Rule”

… Communicate Worldwide on Internet to Share Knowledge and Ideas, and to fast track Implement Problem Solutions that can produce and perpetuate quality of life on earth

… Practice Compromise and Never Jeopardize Integrity

… Work Together throughout the world to produce and perpetuate a better future